1. Field of the Invention
The present invention relates to a driving circuit including plural amplifier for applying a variable voltage signal to plural capacitive loads respectively in such case as applying driving signal to plural electrodes of a display apparatus.
2. Description of the Related Art
There is a plane type cathode ray tube display apparatus as one example of the display apparatus employing a driving circuit including plural amplifier for applying a variable voltage signal to plural capacitive loads respectively. As shown in FIG. 5, this display apparatus comprises plural electrodes arranged as layers in the vacuum container (the vacuum container is not drawn in FIG. 5). In FIG. 5, there are a back plate 1, a liner cathode 2 as an electron beam source, an electron beam attracting electrode 3, an electron beam control electrode 4, a horizontal deflection electrode 5, a vertical deflection electrode 6, and a screen board 7 sequentially arranged from the rear side of the display apparatus to the front screen side.
Each liner cathode 2 as the electron beam source is installed in a horizontal direction and the plural number (19 for instance) liner cathode 2 are arrayed in the vertical direction by the predetermined intervals (for instance, 4.4 mm). Seven liner cathodes 2a to 2g are shown in the figure in FIG. 5 for instance. Each liner cathode 2 emits an electron beam which is distributed in a horizontal line. The electron beams are emitted sequentially during predetermined time (8H) beginning from the top liner cathode 2a and shifting to down to the next liner cathode in order as shown in FIG. 6. In FIG. 6, the electron beam discharge period corresponds to the period when the liner cathode driving pulse is at a L level.
The back plate 1 makes the electron beam emitted from the liner cathode go to the anode side (viewer side) by applying a negative DC voltage, and suppresses the generation of the electron beam from the liner cathodes except for the liner cathodes presently driving.
Through-holes 10 are horizontally formed with a predetermined pitch at the position opposing to the corresponding liner cathodes 2a to 2g of the electron beam attracting electrode 3. By applying positive DC voltage to the electron beam attracting electrode 3, the electron beam emitted from the liner cathode 2 are accelerated, and the electron beam is drawn out through the through hole 10.
The Electron beam control electrode 4 includes plural conductive plate 13 (for instance 114) arrayed in a vertical direction with predetermined pitch, where each conductive plate is arranged in a horizontal direction as shown in FIG. 5. For instance, only eight conductive plates 13 are shown in FIG. 5. Through holes 12 are formed in the electron beam control electrode 4 corresponding to the through hole 10 in the electron beam attracting electrode 3. The electron beam control electrode 4 controls the amount of the electron beam flow according to the picture signal, which electron beam is drawn out through the through hole 10 installed in the electron beam attracting electrode 3 by applying voltage corresponding to the picture signal.
The horizontal deflection electrode 5 consists of plural conductive plates whose shape is long in the vertical direction, and which are installed in the position sandwiching the electron beam passing through the through hole 12 of the electron beam control electrode 4 alternately. Plural pairs of conductive plates 14 and 14' are arrayed in the horizontal direction according to the predetermined horizontal pitch of the through hole 12 of the electron beam control electrode 4. Horizontal deflection voltage h and h' (about 100 Vpp) which varies step-wise with the opposite phase as shown in FIG. 6 are applied to the pair of conductive plates 14 and 14'. The electron beam corresponding to each pixel is horizontally scanned and focused onto 3 color fluorescent elements R, G, B in the fluorescent layer which is formed on the screen 7 for luminescent. For instance, by horizontal scanning, one electron beam can control luminescent of two sets of 3 fluorescent elements.
The vertical deflection electrodes 6 are the conductive plates whose shape is long in the horizontal direction, and which are installed in the position sandwiching the electron beam passing through the through hole 12 of the electron beam control electrode 4 alternately. Plural pairs of conductive plate 15 and 15' are arrayed in the vertical direction according to the predetermined vertical pitch of the through hole 12 of the electron beam control electrode 4. Each conductive plate is arrayed by predetermined pitch in the vertical direction. Vertical deflection voltage V and V' (about 350 Vpp) which varies step-wise with the opposite phase as shown in FIG. 6 is applied to the pair of conductive plates 15 and 15'. The electron beam is deflected (scanned) by the vertical deflection voltage. For instance, one electron beam can control 12 lines of fluorescent elements by the vertical scanning. 20 conductive plates can compose 19 pairs of conductive plates corresponding to the 19 liner cathodes. Therefore, 228 lines of horizontal scanning line can be displayed on the screen 7.
Screen 7 is composed of glass plate. Fluorescent elements are coated onto the back plane of the screen 7. Each fluorescent element R, G, B is coated as slender stripe shape in the vertical direction sequentially to the horizontal direction. High voltage (about 10 kV) is applied to the screen 7. In FIG. 5, horizontal broken line drawn on the screen 7 shows the division of the vertical direction corresponding to plural liner cathodes 2, and vertical broken line drawn on the screen 7 shows the division of horizontal direction corresponding to plural electron beam control electrodes 4.
In the above mentioned embodiment of the display apparatus, both deflection voltage, the horizontal deflection voltage h, h') which is applied to a pair of conductive plates 14 and 14' composing the horizontal deflection electrodes, and the vertical deflection voltage (v, v') which is applied to a pair of conductive plates 15 and 15' composing the vertical deflection electrodes, are obtained by amplifying small voltage signal Vin to Vout by a transistor amplifier as shown in FIG. 7.
Regarding the horizontal deflection electrode and the vertical deflection electrode in the above-mentioned structure of display apparatus, it is difficult to reduce the capacitance of these electrodes. In order to apply the voltage signal which varies with large amplitude to a such capacitive load, the voltage signal has been amplified with the above-mentioned amplifier. However, the electric power consumption for the amplifying becomes large. For instance, this large electric power consumption will be a problem especially when driving the display apparatus in the portable equipment by battery.